This invention relates to renewable power systems and, more particularly, to renewable power systems using concentrated brine as the energy storage medium.
All heat engines utilize a temperature differential to produce power. Reciprocating engines produce a hot gas and, after the power stroke, dump the remaining energy to a lower temperature environment. The Rankine cycle relies on two heat reservoirs at different temperatures. The idea of using the warm ocean surface and the cold deep ocean as two heat reservoirs was proposed as early as 1901 by d'Aronval.
The concept of the present invention is based on a large scale absorption cycle using a concentrated salt solution or other hygroscopic solution, herein referred to as "brine," as an energy storage medium. As used herein, brine means a water solution of salts (acid, alkaline or neutral). Basically, energy is stored in brine by evaporating solvent, e.g., water, from the solution, whereby the salt is concentrated and the brine has a vapor pressure that is low compared to pure solvent. If a source of the pure solvent and a source of concentrated brine are placed so that the volumes above the solvent and brine are in communication at about the same initial temperatures, vapor from the solvent will condense on the brine due to the low vapor pressure adjacent the brine. The evaporation of solvent extracts a latent heat of vaporization from the solvent, lowering the solvent temperature. The condensation of solvent vapor on the brine deposits the latent heat of vaporization in the brine, raising the brine temperature. This process continues until a temperature difference arises that equalizes the vapor pressure above the solvent and above the brine. See, e.g., N. Isshiki, "The Concentration Difference Energy System," 2 J. Non-Equilb. Thermodyn., No. 2, pp. 85-107 (1977), incorporated herein by reference.
Useful energy can now be extracted from the brine. isshiki, supra, and Assaf in U.S. Pat. No. 4,617,800 propose series and parallel boiler arrangements, respectively, to extract energy from the brine. In both cases the brine is used only once. Assaf proposes a heat exchanger with a heat conductive barrier that separates the heat exchanger into two compartments, one of which constitutes the condenser side, and the other of which constitutes the evaporator side. Concentrated brine from the brine source is caused to fall in a film on the condenser side of the barrier for effecting condensation of the heat depleted vaporized working fluid, such condensation releasing the latent heat of condensation to the brine, which is warmed as it is diluted. Liquid working fluid from a source is caused to fall in a film on the evaporator side of the barrier. Heat from the warmed brine film is transferred through the barrier to the cooler film of liquid working fluid, which, in the reduced pressure of the evaporator side, flashes into vapor that is conducted to a turbine. Since Assaf interfaces the brine with the heat depleted vaporized working fluid, the system is usable only with water as the working fluid.
Isshiki teaches a series of chambers operated at progressively higher pressure and temperature to form a steam for running a turbine. Exhaust from the turbine is used to heat the brine in one of the stages. Again, brine is injected into the stages in parallel so that a brine solution is used only once.
A source of concentrated brine is required with stored energy in the form of the concentrated salt. U.S. Pat. No. 4,704,189 to Assaf contemplates the use of large spray towers for converting solar energy to "concentration energy" as a dilute brine is sprayed in the direction of a prevailing air flow with a concomitant loss of the evaporated water from the brine solution. Isshiki contemplates the use of waste heat from various sources to provide the energy that is converted to concentration energy.
Accordingly, it is an object of the present invention to provide for extracting energy from the brine at one or more dilution stages.
It is another object of the present invention to provide a non-aqueous working fluid for driving a turbine, expander, or the like.
One other object of the present invention is to optimize the use of hot dry air to concentrate the brine wherein the solar energy in the air is converted to concentration energy in the brine.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.